What Is A Two-Stage Ditch?

A two-stage ditch design commonly features a low flow channel and a constructed “bench.”  An effective bench is expected to ensure long term stability in the channel.  An increase to the width of the channel, through the bench construction and consequential bank shaping, aids in preventing over-bank flow during normal storm events.  The goal of improved drainage function is generally realized through a more stable channel profile that reduces the cost of periodic maintenance.  From a water quality perspective, the two-stage ditch design offers benefits in restoring some flood plain function, improved sediment transport and capture, better nutrient and pollutant processing, and increased aquatic habitat and communities.  The two-stage ditch practice has been presented for several decades as a viable alternative for marrying drainage improvement with improved water quality.  In the last decade, a number of demonstration sites have been established across the region for the purpose of researching the practice.